LED illumination systems

ABSTRACT

An illumination system includes a power supply having a boost converter operating in the discontinuous conduction mode, a flyback converter operating in the critical conduction mode, and a switch coupled to the flyback converter. Several light emitting diodes receive power from the power supply. The boost converter may include a boost inductor (L B ) and a boost diode (D B ), constructed to perform the boost power factor correction (PFC) function. The flyback converter may includes a flyback inductor (L FB ) and a flyback diode (D FB ) and the power supply may be constructed to turn on the switch around the point where the current flowing in the flyback inductor reaches zero value.

This application claims priority to U.S. Application 61/395,200, filedon May 8, 2010, entitled ILLUMINATION SYSTEMS, which is incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to illumination systems and methods usinglight emitting diodes (LEDs), and more particularly relates toillumination systems and methods using novel power supplies,controllers, and LED modules.

Commercial lighting systems, used on the outside of commercial buildingsfor advertising purposes, include channel letters. Channel lettersgenerally include a housing with a concave cross-section about 5″ deep,made of aluminum or plastic. The housing cavity, shaped as the letter,is covered by a translucent plastic sheet of a selected color,illuminated by a light source mounted within. Neon and fluorescentlights provide suitable illumination, allowing the letters to shinebrightly when turned on. However, fluorescent light sources have arelatively short life of approximately 20,000 hours. They operate athigh voltage (for example, 7,000 to 15,000 volts for neon) and canconsume a relatively large amount of electrical power. Furthermore,fluorescent light tubes are usually quite fragile. Still, fluorescentlights have been used for decades and decades in different fields.

Light emitting diodes (LEDs) are currently used for a wide range ofapplications, providing a variety of advantages relative to conventionallights, such as neon or fluorescent bulbs, due to their advantageousqualities. LEDs are compact, rugged, and consume less power, being 30 to70% more energy efficient than conventional lights. LEDs have arelatively long life of up to 100,000 hours and operate at low voltages(4 VDC to 24 VDC).

LED illuminating system generally used in commercial, architectural,home or landscaping applications usually include a DC power supplyusually connected to 110 VAC (220 VAC). The output from the power supplyprovides DC voltage (usually from 4 VDC to 24 VDC) to a supply rail,wire, or connectors providing electrical connection to LED arraysarranged in several illumination modules also including ballastresistors. These modules are usually connected in parallel on a DCsupply bus. The LEDs are connected with wires that are solderedpermanently at a fixed spacing, or using electrical connectors providinguse fixed electrical contact; that is, use fixed electrical wiring.Every single illumination module is connected to the next module usingtwo or four wires (i.e., positive and negative inputs and outputs) bymechanically creating electrical contact. Each LED module uses a ballastresistor (or regulator) to provide a constant current to the LEDsconnected in series since LEDs operate with current (and not voltage).The modules are usually located inside a letter channel. Thisdissipative method normally uses as much energy in the ballast resistor(i.e., dissipated energy) as in the LEDs, resulting in efficienciessometimes even lower than 50%. This means there is frequently asignificant amount of energy wasted in heat.

The brightness of an LED depends upon the amount of electrical currentflowing through the diode. However, while an increase in currentincreases the brightness of the light emitted by the LED, it alsoincreases the connection temperature, which can decrease the LED'sefficiency and life. Given that LEDs are often constructed ofsemiconductor materials that share many comparable properties withsilicone and gallium arsenide, this can be highly detrimental.

The conventional light circuits can be prone to problems other thanthose described above. The LED modules joined physically using fixedelectrical contact connectors, which are prone to reliability troubles.For example, connectors can fail due to corrosion, and many devices, aswell as commercial lighting systems, are used outdoors. Also, whilediodes are generally biased through a series resistor from a regulatedvoltage supply, the amount of current going through the diode dependsalso on the forward voltage drop over the diode, which drops withchanges in its size, age, and its temperature at the time.

The LEDs have been also used as light sources in applications such asemergency EXIT signs. The EXIT signs contain a reflector in the rear,having a series of curved, concave surfaces shaped as letters andbackground area. The LEDs are mounted in the center of each surface toprovide light that is projected outwardly. The LEDs have been used forillumination and in architectural and gardening designs where therobustness of the illumination system and life of the illuminationsystem is very important since repair or replacement requiressignificant cost of labor (even sometimes surpassing the cost of the LEDsystem).

There is still a need for an improved illumination system that is simpleand quick to install and that operates at relatively high powerefficiency.

SUMMARY OF THE INVENTION

The present invention relates to LED illumination systems and methodsusing novel converter power supplies, controllers, and/or LED modules.

According to one aspect, an illumination system includes a power supplyhaving a boost converter operating in the discontinuous conduction mode,a flyback converter operating in the critical conduction mode, and aswitch coupled to the flyback converter. Several light emitting diodesreceive power from the power supply.

Preferred embodiments of this aspect include one or several of thefollowing features: The boost converter includes a boost inductor(L_(B)) and a boost diode (D_(B)) and is constructed to perform theboost power factor correction (PFC) function. The flyback converterincludes a flyback inductor (L_(FB)) and a flyback diode (D_(FB)) andthe power supply is constructed to turn on the switch as the currentflowing in the flyback inductor reaches zero value. Alternatively, theoutput from the flyback converter may be constructed to turn on theswitch before or after the point where the current flowing in theflyback inductor reaches zero value.

The output of the flyback converter is used for regulating the powersupply. The flyback converter includes a capacitor operating in openloop and thus the power supply is controlled without receiving afeedback from the capacitor of the flyback converter. All capacitorsused in the power supply are non-electrolytic capacitors.

The flyback converter provides an output being regulated by a feedbackloop. The flyback converter is regulated by a voltage feedback. Theflyback converter is regulated by a current feedback. The flybackconverter is regulated by the feedback loop and an error signal sets apeak current of the flyback inductor (L_(FB)) that automatically alsodetermines a current flowing in the boost inductor (L_(B)).

The flyback converter includes a flyback inductor (L_(FB)), a switch(Q), and flyback diode (D_(FB)) providing flyback-based outputregulation and isolation.

The output from the flyback converter is coupled to an output rectifierand a filter providing an LED current to the several light emittingdiodes. The LED current is similar to an ideal current source.

The illumination system includes an illumination module including anelectromagnetic coupling element and the several light emitting diodes,wherein the electromagnetic coupling element includes a magnetic corearranged to receive output current from the power supply over acurrent-carrying loop forming a primary wire. A secondary wire is woundwith respect to at least a portion of the magnetic core to enableinductive coupling from the primary wire, and provide a current to theseveral light emitting diodes.

The illumination system may include a second illumination moduleincluding an electromagnetic coupling element and the several lightemitting diodes, wherein the electromagnetic coupling element includes amagnetic core arranged to receive output current from the power supplyover a current-carrying loop forming a primary wire. A secondary wire iswound with respect to at least a portion of the magnetic core to enableinductive coupling from the primary wire, and provide a current to theseveral light emitting diodes.

The magnetic core and a part of the secondary wire wound around the coreare encapsulated, thereby sealing the core and wire portion whileenabling displacement of the primary wire with respect to theencapsulated magnetic core. The magnetic core may be ring-shaped and thesecondary wire is wound around at least a portion of the ring-shapedcore. The primary wire is threaded through an opening in the ring-shapedcore.

The magnetic core may have a rectangular shape, and the secondary wireis wound around at least a portion of the rectangularly-shaped core. Theprimary wire is threaded through an opening in the rectangularly-shapedcore.

According to another aspect, an illumination system includes a masterpower supply including a boost converter and a flyback converter, and anillumination module. The master power supply is constructed and arrangedto generate high-frequency and low-voltage electrical power provided toa primary wire forming a current-carrying loop. The illumination moduleincludes an electromagnetic coupling element and several light emittingdiodes, wherein the electromagnetic coupling element includes a magneticcore arranged to receive the current loop, and a secondary wire woundaround at least a portion of the magnetic core to enable inductivecoupling from the primary wire. The secondary wire is connected toprovide current to several light emitting diodes.

Preferred embodiments of this aspect include one or several of thefollowing features:

The magnetic core and a portion of the secondary wire wound around thecore are encapsulated thereby sealing the core and the wire portionwhile enabling displacement of the primary wire with respect to theencapsulated magnetic core. The magnetic core is ring-shaped, and thesecondary wire is wound around at least a portion of the ring-shapedcore. The primary wire is threaded through an opening in the ring-shapedcore.

Alternatively, the magnetic core has a rectangular shape, and thesecondary wire is wound around at least a portion of therectangularly-shaped core. The magnetic core may include at least twoparts forming the rectangular shape. The primary wire is placed in theopening of the rectangularly-shaped core by removing one of the parts.

Alternatively, the magnetic core is shaped to include a closed magneticpath, and the secondary wire is wound around at least a portion of thecore to provide electromagnetic coupling.

According to yet another aspect, an illumination system includes amaster power supply including an AC inverter and an amplitude modulator.The master power supply is constructed and arranged to generatehigh-frequency current provided to a primary wire forming acurrent-carrying loop. The amplitude modulator is constructed toamplitude modulate the current (l_(loop)) at least two modulationfrequencies. The illumination system also includes at least twoillumination modules each including several light emitting diodesreceiving power by inductive coupling from the current-carrying loop.Each the illumination module includes a frequency discriminator,responsive to one of the modulation frequencies, constructed to enablecontrol of a DC current to the light emitting diodes and thereby controlemission of light from the light emitting diodes.

Preferred embodiments of this aspect include one or several of thefollowing features:

The inductive coupling is achieved by an electromagnetic couplingelement including a magnetic core arranged to receive thecurrent-carrying loop as a primary wire. A secondary wire is woundaround at least a portion of the magnetic core to enable the inductivecoupling from the primary wire. The secondary wire is connected toprovide current to the light emitting diodes.

The high-frequency current (l_(loop)) is in the range of 20 kHz to 100kHz, and the modulation frequencies are in the range of 1 kHz to 10 kHz.Several modulating signals can be introduced this way using frequencymultiplexing.

The illumination module comprises a decoding hardware includes a diodebridge a frequency discriminator, a rectifier, and a comparatorproviding its output signal to a switch. The switch that acts as anon/off shunt for the light emitting diodes.

The illumination system includes a master power supply that includes aresonant inverter. Preferably, the inverter provides an output in therange of about 20 kHz to about 40 kHz. Preferably, the master powersupply includes a self-oscillating inverter providing substantially asine wave output.

According to yet another aspect, an electromagnetic coupling element isused with an illumination system. The coupling element is constructed tocouple inductively power from a power supply to one or multiple lightsources. The coupling element includes a magnetic core, a source wirewound around at least a portion of the magnetic core and being connectedto at least one light source, and a casing surrounding the magnetic coreand the source wire at the portion being wound around the magnetic coreto electrically insulate the source wire and the magnetic core. Thecoupling element also includes an inductive region defined by themagnetic core and arranged to receive a conductor in a removablearrangement with respect to the magnetic core, the conductor beinglocated to couple inductively power from a power supply to the sourcewire.

According to yet another aspect, a master power supply is designed foran illumination system. The master power supply includes a resonantinverter, and an AC current source. The resonant inverter is constructedand arranged to generate a high-frequency and low-voltage electricaloutput. The AC current source includes an inductor and provides power toa current-carrying loop.

Preferred embodiments of this aspect include one or several of thefollowing features: Different embodiments of the master power supply,including a resonant inverter, and an AC current source are described inU.S. application Ser. No. 11/786,060, now U.S. Pat. No. 7,928,664, whichis incorporated by reference as if fully reproduced herein.

Preferably, the master power supply includes a microcontroller. Themaster power supply can include a power factor corrector, a pulse widthmodulation (PWM) line regulator a loop current sensor, or an opencircuit voltage sensor.

The illumination system includes at least two illumination modules eachincluding several light emitting diodes receiving power by inductivecoupling from the current-carrying loop. Different illumination modulesare also described in U.S. Pat. No. 7,928,664 and may be used with thepower supplies described here or described in U.S. Pat. No. 7,928,664.

According to yet another aspect, an illumination method includesgenerating high-frequency and low-voltage electrical power; providingthe high-frequency and low-voltage electrical power to a primary wireforming a current loop; coupling energy from the current loop in acontactless manner to a secondary wire; and delivering current from thesecondary wire to several light emitting diodes (LEDs).

Preferably, the illumination method includes controlling thehigh-frequency and low-voltage electrical power, and/or sensing a loopcurrent by monitoring output of the high-frequency and low-voltageelectrical signal, and/or sensing an open voltage current.

According to yet another embodiment, in an illumination system, aninstallation method is used for contactless coupling one or severalillumination modules to a power supply. The illumination systemcomprises a master power supply constructed and arranged to provideelectrical power to a primary wire forming a current loop; and anillumination module including an electromagnetic coupling element andseveral light sources. The electromagnetic coupling element includes amagnetic core. The method includes positioning one or several of theillumination modules constructed to provide light; and positioning theprimary wire in a close proximity to the illumination module withoutestablishing an electrical connection, the positioning enablinginductive power transfer from the primary wire to a secondary wire woundaround at least a portion of the ferromagnetic core, wherein thesecondary wire is connected to provide current to one or multiple LEDs.

According to yet another embodiment, an illumination system may includea master power supply providing power to several illumination modules.The master power supply is constructed and arranged to generatehigh-frequency and low-voltage electrical power provided to a primarywire forming a current loop. Each illumination module includes anelectromagnetic coupling element and several LEDs. The electromagneticcoupling element includes a magnetic core arranged to receive thecurrent loop in a removable arrangement, and a secondary wire woundaround the magnetic core to enable inductive coupling. The secondarywire is connected to provide current to the LEDs.

Preferred embodiments of this aspect include one or several of thefollowing features: The magnetic core and a part of the secondary wirewound around the core are encapsulated, thereby sealing the core andwire portion while enabling displacement of the primary wire withrespect to the encapsulated ferromagnetic core.

The magnetic core is formed from two or more discrete elements assembledto provide a closed magnetic loop. The secondary wire is preferablywound around a portion of the magnetic core and the construction enablesdisplacement of the primary wire with respect to the ferromagnetic core.The magnetic core may be made of a ferromagnetic material, a ferrite, ora soft ferrite.

The illumination system of this aspect has numerous advantages: There isno need to establish electrical contact or connection to any of theillumination modules, thus increased reliability, lower cost, notposition dependent. The system has high efficiency (relatively low powerconsumption by the elimination of the ballast resistor used for LEDs inprior art systems. There is only one wire used for powering theillumination modules instead of two or four wires in the prior artilluminations systems. Quick and easy installation since there is nopolarity because of using alternating current provided by the masterpower supply. The system can be truly waterproof when the illuminationmodule is encapsulated since there is no connection to the outsideworld. This provides greater installation safety due to the absence ofvoltage nearby which prevents accidental contact, and since there is notouchable connection or soldering accessible.

Further features and advantages of the present invention as well as thestructure and method of various embodiments of the present invention aredescribed herein in detail below, with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates diagrammatically a converter power supply for an LEDillumination system.

FIG. 2 illustrates diagrammatically another embodiment of a power supplyfor an LED illumination system.

FIG. 3 illustrates diagrammatically another embodiment of a power supplyfor an LED illumination system.

FIG. 3A illustrates diagrammatically another embodiment of a powersupply for an LED illumination system.

FIG. 4 illustrates a schematic diagram of the converter power supplyusing a single switch.

FIG. 5 illustrates a schematic diagram of another of the converter powersupply using two switches.

FIG. 6 illustrates another embodiment of the power supply using a singleswitch for controlling current output to several LEDs.

FIG. 6A illustrates an illumination module, for use with the powersupply of FIG. 6, designed to provide dimming for the connected LEDs.

FIG. 7 illustrates another embodiment of the power supply using twoswitches for controlling current output to several LEDs.

FIGS. 7A and 7B are graphs that illustrate operation of the power supplyshown in FIGS. 7 and 8.

FIG. 8 illustrates another embodiment of a power supply for an LEDillumination system designed for several modules each having severalLEDs, each module receiving power by contactless coupling.

FIG. 8A illustrates a module having several LEDs and receiving power bycontactless coupling.

FIG. 9 illustrates another embodiment of a power supply for use withseveral LED illumination modules having contactless coupling.

FIG. 10 is a circuit diagram of a power supply for use with a string ofLEDs.

FIG. 11 illustrates an illumination system including an AC currentinverter, an amplitude modulator and several illumination modules havingcontactless coupling, each illumination module being separatelycontrolled by amplitude modulation.

FIG. 12 illustrates one illumination module shown in FIG. 11.

FIG. 13 illustrates one embodiment of the AC current inverter and theamplitude modulator shown in FIG. 11.

FIG. 14 illustrates one embodiment of an oscillator for use in the ACcurrent inverter shown in FIG. 11.

FIG. 15 is a circuit diagram of a power supply for use with severalillumination modules having contactless coupling, each illuminationmodule being separately controlled by a characteristic frequency.

FIG. 16 illustrates a contactless coupling element for use with theillumination systems shown in FIG. 8, 9, or 11.

FIG. 16A illustrates another embodiment of a contactless couplingelement having a magnetic core formed by two discrete elements and beingsuitable for use with the illumination systems shown in FIG. 8, 9 or 11.

FIG. 17 illustrates a string of LEDs for use with the illuminationsystem of FIG. 6 or 7.

FIG. 17A illustrates one illumination module used with the illuminationsystem of FIG. 8, 9 or 11, and having a contactless coupling elementshown in FIG. 16 or 16A.

FIG. 17B illustrates several illumination modules for multicolorillumination used with an illumination system providing severalcurrent-carrying loops.

FIG. 18 illustrates an illumination system including an AC currentinverter and several illumination modules installed in a letter channeland a power supply.

FIGS. 19 and 19A illustrate a coupling box for use with the illuminationsystems shown in FIG. 8, 9 or 11.

FIGS. 19B and 19C illustrate schematically a magnetic core and locationsof secondary wires inside the coupling box shown in FIGS. 19 and 19A.

FIGS. 20, 20A, 20B and 20C illustrate different embodiments of thecoupling boxes designed for the illumination systems shown in FIG. 8, 9or 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to LED illumination systems andmethods using novel converter power supplies. FIGS. 1, 2, 3 and 3A,illustrate diagrammatically different embodiments of converter powersupplies used with LED illumination systems. Converter power supplies10, 10A, 10B and 10C include a rectifier bridge 12, a boost cell 14 (aboost converter 14), a flyback cell 16 (a flyback converter 16), and anoutput rectifier and filter 20 connected to a string of light emittingdiodes (LEDs). Converter power supply 10A includes, instead of a singlerectifier and filter cell 20, a series of resonant converters arrangedfor open-loop operation 22 and connected to several rectifier and filtercells 24 ₁, 24 ₂, . . . , and 24 _(N) coupled by transformers T_(M1),T_(M2), . . . , and T_(MN). Each output rectifier and filter cellprovides current to a string of LEDs. The rectifier and filter unittogether with the string of LEDs may be packaged as an illuminationmodule, described below. Rectifier bridge 12 may be replaced with a DCsource.

FIG. 4 illustrates a high level schematic diagram of a converter powersupply 50 utilizing a single switch as illustrated by a switch 18 inFIGS. 1 and 2. FIG. 5 illustrates a high level schematic diagram of aconverter power supply 60 utilizing a dual switch as illustrated byswitches 35 and 36 shown in FIGS. 3 and 3A, respectively. The switchesare controlled in a feedback arrangement from the output (illustrated as28) using a controller 30.

FIG. 6 illustrates diagrammatically another embodiment of a converterpower supply 70 for an LED illumination system. Converter power supply70 includes the boost cell including L_(B), Q, D_(B) and a capacitor Cfor performing the boost-PFC function. Converter power supply 70includes the flyback cell including L_(FB), Q, D_(FB) and C_(o),performing a flyback-based output regulation and isolation function.Converter 70 is controlled by a single loop, where the feedback variableis the average flyback output current. The flyback output current can besensed by a resistor or, more conveniently, by a current transformer.Appropriate compensation can be added to this loop to either eliminateor attenuate the output ripple current so that both input and outputcurrent wave shapes are acceptable.

In converter power supply 70, the inductance ratio of the values ofL_(B) and L_(FB) is sized in such a way that the boost converteroperates in the discontinuous conduction mode (DCM), where the inductorcurrent L_(B) is always at zero before the switch is turned on, as shownin FIGS. 7A and 7B. Furthermore, the flyback converter operates in thecritical conduction mode (CC mode), where the switch Q is turned back onas soon as the L_(FB) inductor current reaches zero. In this mode ofoperation, it is established that the bulk capacitor voltage is anapproximately linear function of the input line voltage, and it istherefore automatically limited. At the same time, the effect of loadchanges is automatically and quickly followed at the input. (See FIGS.7A and 7B.) This is not the case for typical two-stage convertersproposed by others, where the PFC pre-regulator suffers fromconsiderable lag.

Importantly, the converter power supplies shown in the presentembodiments do not use the bulk voltage as feedback at all, but use theoutput of the flyback converter as feedback for regulation. Instead,absolutely no feedback is used from the bulk capacitor, its voltage isdictated instead again by the ratio of L_(B)/L_(FB) and is open loop.Therefore, the value of capacitor C can be very small for the sameoutput power and a large amount of ripple can be tolerated. Oursimulation shows 200 v PP of ripple on 375 Vdc. In the converter powersupplies shown in the present embodiments the capacitor value isapproximately 1/50 (i.e., 2%) of the value it can now be a 1 μF (microFarad) film type capacitor that has an extremely long life that matchesthe LED mtbf 100,000 hrs.

The output of the flyback converter is regulated (voltage or currentfeedback depending on the application) and the error signal sets theflyback inductor L_(FB) peak current that automatically also determinesthe boost inductor L_(B) current. The flyback that is regulated has noline frequency ripple at the output as can be seen in the simulation,all the line ripple is on the boost capacitor C instead.

The output circuit of a flyback cell is similar to an ideal currentsource, assuming that C_(o) is small. Because this is the case in thistopology, and the controlled variable is the output current,compensation of the feedback loop is relatively simple. It can be madefast and stable so that the converter can address variations in theoutput parameters very effectively.

Another advantage of using the current sourced output provided by theflyback, validating its adoption for this application, is itsflexibility when dealing with widely varying output voltages, as is thecase with LED strings of variable lengths.

This topology offers the following main advantages:

(1) The DC bulk voltage on capacitor C is independent of output loadpower and can be mostly determined simply by a judicious choice of L_(B)and L_(FB) for a given line voltage. In the specific embodiment shown,the values are L_(B)=1.5 mH and L_(FB)=9 mH, for the output power of 18W, the input line voltage 120 Vac, and V_(B) voltage 375 V.

(2) A single control loop can eliminate the output ripple current evenin the presence of large voltage ripple on capacitor C. This allows C tohave a small value, making it possible to use high reliability plasticfilm technology.

(3) The power factor and input current THD are naturally good even inthe absence of a dedicated input current control loop. Rather, the inputcurrent wave-shaping function is automatically performed by the outputcontrol loop; however, the intrinsically accommodating open-loopbehaviour of the boost cell operated in DCM allows the power factor toremain acceptable.

(4) As mentioned, the DCM-boost/CC-flyback topology allows for excellentdynamic behavior. Furthermore, the load power level has minimal effecton the bulk voltage of C. Because of these advantages, the load powercan be transitioned seamlessly at the output, allowing a simple andinexpensive way of performing the dimming function by simply shortingout the flyback transformer at a given duty ratio using a transistor, asshown in FIG. 6A.

Referring to FIG. 6A, module 80 includes a topology that adds, only aninductor and a diode, and uses a simple plastic capacitor, C_(o).Furthermore, the topology allows for a very simple and inexpensivedimming concept. A small transistor may be employed for shorting out theLED string directly for the dimming purposes.

The present converter power supplies provide input current shaping butsometimes do not eliminate completely the line current distortion.However, even in this case the distortion level meets the common linequality standards applicable to the industry or residential settings.This desirable performance is achieved without the use of anyelectrolytic capacitor while preventing the current ripple from flowingin the LED string.

FIG. 7 illustrates diagrammatically an improved embodiment of theconverter power supply shown in FIG. 6. Converter power supply 100includes an auxiliary self-driven switch, Q_(A). This added switchrequires no additional drive or control and it is simply a way tooptimize semiconductor utilization. In fact, in the basic circuit 70(FIG. 6), the single switch Q absorbs the sum of the currents from theboost and flyback cells as well as the sum of the voltages from theboost and flyback cells. Thus, the single switch Q needs to berelatively larger as compared to two switches Q and Q_(A), which couldhave reduced voltage ratings.

In converter power supply 100, switch Q only absorbs the voltage stressrelating to the boost cell, whereas Q_(A) only absorbs the voltagestress relating to the flyback cell. For typical operation, calculationsand simulations show that a single 1000V field-effect transistor (FET)can be substituted by two 500V FETs with a substantial gain in overallefficiency and cost.

Converter power supply 100 provides a resonant turn-on. Because theflyback cell is operated in critical conduction, switches Q and Q_(A)turn on immediately following the complete discharge of the flybackcoupled inductor L_(FB). (See FIGS. 7A and 7B.) Given enough time, theleakage inductance of L_(FB) will ring with the parasitic capacitance ofQ. The frequency of this ring is known so that a precise delay can beadded following the discharge. If this delay is made to correspond toapproximately ¼ period of the ringing, the FETs will turn on whilesupporting minimal voltage, thus reducing switching loss. This effectwill be more substantial at higher loads when overall dissipation iscritical.

FIGS. 7A and 7B are graphs that illustrate operation of the power supplyshown in FIGS. 7 and 9, wherein FIG. 7A illustrates the relationship ofthe input voltage (V_(IN)), bulk voltage (V_(B)) and the output voltage(V_(OUT)) voltage V_(B) voltage V_(B) voltage. In converter power supply70, the inductance ratio of the values of L_(B) and L_(FB) is sized insuch a way that the boost cell operates in the discontinuous conductionmode (DCM), where the inductor current L_(B) is always at zero beforethe switch is turned on, as shown in FIGS. 7A and 7B. Furthermore, theflyback cell operates in the critical conduction mode (CC mode), wherethe switch Q is turned back on as soon as the L_(FB) inductor currentreaches zero (AL2). In this mode of operation, it is established thatthe bulk capacitor voltage (V_(B)) is an approximately linear functionof the input line voltage; it is therefore automatically limited. At thesame time, the effect of load changes is automatically and quicklyfollowed at the input. (See FIGS. 7A and 7B.) This is not the case fortypical two-stage converters where the PFC pre-regulator suffers fromconsiderable lag.

FIG. 8 illustrates another embodiment of a power supply for an LEDillumination system designed for several modules each having severalLEDs, each module receiving power by contactless coupling. FIG. 8illustrates another embodiment of a converter power supply designed foruse with several LED illumination modules having contactless coupling,as described in detail below. Converter power supply 70 is coupled to anDC to AC conversion cell 75 that provides current to a current-carryingloop 210 (that is, a primary current loop 210). Several illuminationmodules 202A, 202B, . . . 202N are coupled in a contactless manner tothe using current loop 210 using the corresponding transformers T_(M1),T_(M2), . . . , and T_(MN). Each illumination module includes anelectromagnetic coupling element (shown in detail in FIG. 16 and FIG.16A) and several light emitting diodes (LEDs).

FIG. 8A illustrates a module having several LEDs and receiving power bycontactless coupling. Illumination module 280 includes theelectromagnetic coupling element (shown in detail in FIG. 16 and FIG.16A), an AC to DC converter 204, a series of LEDs, and an output forcurrent sensor used for diagnostic purposes. The electromagneticcoupling element receives primary wire 210 and provides secondary wireoutput across capacitor C1 to AC to DC converter 204. AC to DC converter204 includes four high-speed double diodes CR1, CR1 a, CR2 and CR2 a(BAV99 made by Philips Semiconductors). The strip 206 includes, forexample, 8 LEDs, each being coupled to a Zener diode. The Zener diodesprovide electrical paths in case an individual LED fails so that theremaining LED can still operate.

FIG. 9 illustrates diagrammatically another embodiment of the converterpower supply. Converter power supply 120 designed for use with severalillumination modules 202A, 202B, . . . 202N coupled in a contactlessmanner to the using current loop 210. Detailed description of theillumination modules 202A, 202B, . . . 202N and the description of thecontactless coupling to the current-carrying loop 210 is provided below.

Converter power supply 120 is designed keeping in mind the safetyregulations pertinent to LED applications limit the accessible outputvoltage for each string to 60V. Therefore, in order to expand thecapacity of the illumination system, many separate channels must beprovided. If converter power supply 120 is designed for multi-channeloperation, each shall include an isolation transformer. The individualchannels may support LED strings of different lengths, thus generatingdifferent flyback voltages. In converter power supply 120, the bulkvoltage V_(B) is derived, as before, using a DCM boost and CC flyback,with all the advantages described earlier. The output of the isolatedflyback, however, is an intermediate bulk voltage V_(I). Thisintermediate voltage feeds a set of output transformers inseries-resonant configuration.

FIG. 10 is a circuit diagram of a converter power supply 100A, accordingto another preferred embodiment. Power supply 100A can provide currentto one or several strings of LEDs. The topology of converter powersupply 180 can be divided basically into 10 units (delineated as unitsA, B, C, D, E, F, G, H, I, and J shown in FIG. 10).

Referring to FIG. 10, the input filter and rectifier (delineated assub-circuit A) rectifies the input line voltage and filters highfrequency noise. Converter power supply 180 utilizes the boost cellincluding a boost choke and a bias transformer (delineated assub-circuit B), which uses a 1.5 mH choke as the boost inductor, whichforms the PFC circuit. A small winding is added in order to produce Vccbias voltage during operation. The boost cell includes a boost switchand boost current limit sub-circuit (delineated as sub-circuit C), whichincludes a boost FET switch and small current sensing resistor, added atits source in order to generate a current sense signal that is used bythe controller for the boost current limiting purpose. The boost cellalso includes a boost diode and output capacitor (delineated assub-circuit D) for providing output of the boost converter. The boostcapacitor is small enough (about 2.2 uF) to be available innon-electrolytic various types of capacitors.

Converter power supply 100A utilizes the flyback cell having a flybacksection delineated as sub-circuit E. The flyback includes a 9 mH flybacktransformer, a pair of FET switches, an output diode and an outputcapacitor. The output capacitor has sufficiently small capacitance to bea non-electrolytic capacitor (of any known design). Importantly, allthree switches are all driven by the same drive pin (that is, pin 7 onthe FAN6961 controller). Therefore, only one main control loop ispresent. This topology allows for the simple integration of the threeswitches into a single switch design. The advantage of using three FETswitches is that each FET switch can be medium voltage and low current,costing less together than the alternative single high voltage highcurrent FET switch.

Converter power supply 100A includes dimmer connections for a dimmermodule that includes a simple PWM type dimmer as shown in FIG. 6A. As isshown diagrammatically in FIG. 6, converter power supply 180 includes acurrent sense delineated as sub-circuit F. The power supply circuitcontrols the output current, which is sensed using a current transformerthat also offers galvanic isolation. This signal is averaged by the RCfilter. This feedback signal is then fed to the controller chip U1 forregulation. The regulator is delineated as sub-circuit G. This circuitdoes not use the internal error amplifier of the controller U1. Ratherand external error amplifier embodied by a shunt voltage referenceTLVH431, which is low-voltage 3-terminal adjustable voltage, used forcontrolling the output current.

Converter power supply 100A includes zero current detector (ZCD)(delineated as sub-circuit I). When the flyback current falls back downto zero following a switch turn-off, the flyback transformer voltagewill reverse polarity. A third winding of the transformer is thereforeadded and used to detect a zero current condition. This signals thebeginning of the next turn-on transition and ensures operation in thecritical conduction mode. The designed circuit conditions this signal sothat it is usable by the controller chip U1. Controller chip U1 is theFAN6961 controller, which is used to generate the driving signals forthe boost and flyback switches. All it needs for this purpose is asignal at pin 5 (zero current detector—ZCD) that becomes active at thetime the flyback current falls back down to zero following a switchturn-off transition.

Converter power supply 100A also includes an over-voltage or over-powerdetector (delineated as sub-circuit J). Here, the same transformerwinding used for the ZCD function is also be utilized to sense theoutput voltage of the flyback, since these are theoretically identicalwhen the flyback switch is turned OFF. When this voltage becomesexcessive, because of overload, the 33V zener diode will break down andallow the control loop to be affected. In fact, the main currentregulating loop will be disrupted and the output current will fold backin order to deal with overload.

FIG. 11 illustrates an illumination system providing separate on/offcontrol of several illumination modules. The illumination systemincludes an AC current inverter 252, an amplitude modulator 254 andseveral illumination modules 260 ₁, 260 ₂, 260 ₃ . . . 260 _(N) havingcontactless coupling to current carrying loop 210 via transformersT_(M1), T_(M2), T_(M3), . . . T_(MN). Each illumination module isseparately controlled by amplitude modulation. This may be used inarchitectural applications, landscaping applications, in groundtransportation vehicles, or in other applications.

AC current inverter 252 produces a high frequency carrier signal 258modulated by several signals, each with a characteristic frequency.Specifically, the carrier signal is in the range of 20 kHz to 100 kHz,and the modulation signal is in the range of 1 kHz to 10 kHz. Amplitudemodulator 254 introduces amplitude modulation (AM) in the currentflowing in the current-carrying loop 210. Several modulating signals canbe introduced this way using frequency multiplexing. The modules containa specific frequency discriminator that responds to only one of theseveral modulating frequencies. Thus each type of module can beactivated in response to a given signal introduced in thecurrent-carrying loop. That is, the amplitude modulated (AM) currentcarrier provides power to the individual LED modules 260 ₁, 260 ₂, 260 ₃. . . 260 _(N), but only those modules that can discriminate their owncharacteristic frequency will actually be enabled and lit up.

FIG. 12 illustrates one illumination module controlled by thecharacteristic frequency. The decoding hardware includes two diodebridges 262 and 264, a frequency discriminator 266, an “ideal” rectifier267, and a comparator 269 providing its output signal to a FET switch235.

Provided by AC current inverter 252, the l_(loop) current is flowing incurrent-carrying loop 210 and is amplitude modulated. The currentinduced in the secondary wire of transformer T_(M) is rectified by twodiode bridges 262 and 264. Diode bridge 262 rectifies the current andproduces a rough 10V bias voltage. Diode bridge 264 rectifies thecurrent to drive an LED string 230A. The LC frequency discriminator 266“recognizes” the presence of the module's characteristic activationfrequency in the drive current signal l_(loop). If the activationfrequency is detected, a large voltage is developed in LC frequencydiscriminator 266 due to resonance. This voltage is rectified byrectifier 267, and compared to a reference voltage 268 in comparator269. Comparator 269 causes the comparator output to turn off the FETswitch 235 that acts as an on/off shunt. Thus, a given LED string is litup only if the activation frequency that is characteristic to its moduleis present in the current l_(loop).

The AM system shown in FIGS. 11 and 12 takes advantage of the relativelyhigh frequency in the current-carrying conductor (20-100 kHz) to providea relatively simple and inexpensive system compared to Power LineCommunication (PLC) systems. The AM system shown in FIGS. 11 and 12avoids adding communication channels on different media alongside thepower connections, does not use superimposed communication signalsinjected at frequencies much higher than the loop current used at 20-100kHz. The present solution also avoids expensive modems and decodinghardware repeated at each module, which is also relatively complex for(PLC) systems.

FIG. 13 illustrates one embodiment of the AC current inverter and theamplitude modulator shown in FIG. 11. The current inverter is in theform of a Royer oscillator 280. Royer oscillator 280 includes atransformer with a primary winding, and a feedback winding. The primarywinding is centre-tapped, with each half driven by a transistorcollector. The feedback winding couples a small amount of thetransformer flux back in to the transistor bases to generate theoscillations. A capacitor across the primary winding gives thetransformer a resonance, which sets the oscillation frequency.

In FIG. 13, inductance L_(L) stabilizes the oscillation voltage into anAC current at high-frequency. This carrier current in the loop has afrequency of the order of 20 kHz-100 kHz. The amplitude of the carriercurrent is controlled by a feedback control loop consisting of a currentsensor 270, which produces a DC voltage proportional to the loopcurrent. This voltage 274 a is compared to a reference voltage 274 b ina comparator 274. The compensated error is provided to a high-frequencypulse with modulator 276 (PWM block 276). The PWM signal is then used todrive FET Q_(R), which, in turn, regulates the average value of voltageV_(D). If the PWM frequency is sufficiently high, Royen oscillator 280operates only by responding to the average value of V_(D), whichdirectly controls the amplitude of the loop current l_(loop) incurrent-carrying loop 210.

In FIG. 13, the reference for the loop current l_(loop) is modified toinclude several low-frequency modulating signals that will appear on thecarrier current. The presence or absence of a given modulating signal isdetermined by a number of control on/off signals (See, Lamp #1, Lamp #2, etc, shown in FIG. 13) provided to a VCO block 281. This way theselective AM modulation is achieved.

FIG. 14 illustrates one embodiment of an oscillator 280A can replaceRoyer oscillator 280 uses in the AC current inverter of FIG. 13.Oscillator 290 includes a pair of drive transistors Q_(x) and Q_(y).This circuit uses a simple bias circuit and couples the gate voltage ofone drive transistor to the drain of the other drive transistor. Thisallows for a simpler construction of the oscillator transformer byremoving the driving winding.

FIG. 15 is a circuit diagram of an HF power supply 300 for use withseveral illumination modules 260 ₁, 260 ₂, 260 ₃ . . . 260 _(N) havingcontactless coupling, as shown in FIG. 11. Each illumination module canbe controlled separately by a characteristic frequency, as explainedabove. High frequency power supply 300 is described in detail in U.S.Pat. No. 7,928,664, which is incorporated by reference as if fullyreproduced herein. The module control can be performed using either anLED module controller 380, or an amplitude modulation unit 385.Amplitude modulation unit 385 provides modulation to the reference forthe current input 354.

Referring to FIG. 15, HF power supply 300 includes an AC to DC converter304, a line frequency sensor 306, a regulator 308, a pulse widthmodulator (PWM) line regulator 320, and a microcontroller 310 receivinga voltage feedback 325 and a current feedback 329. P.W.M. line regulator320 operates at 32 kHz and provides output to a current fed resonantinverter 340. Sine wave resonant inverter 340 receives an enable output338 from microcontroller 310, and resonant inverter 340 provides a 16kHz sinusoidal output 342 to the current source. A current sensor 350 isarranged in a feedback loop to provide an input to microcontroller 310(MC68HC908QY4 made by Motorola Inc.). Furthermore, an open circuitvoltage sensor 360 is connected across the output from resonant inverter340 to signal open circuit condition to microcontroller 310. The ACcurrent source provides a sinusoidal output to current loop 114 via atransformer 370. Microcontroller 310 controls by software the maximumpower output, the maximum output voltage, the loop current and/or otherparameters of the power supply 300. Microcontroller 310 also registersthe fault conditions of the illumination system and adjusts accordinglythe voltage or current provided.

In HF power supply 300, the 110V AC power input is provided to four SMAcontrolled avalanche rectifiers CR4, CR5, CR6, and CR7. Regulator 308includes two (2) NPN switching transistors Q1 and Q2 (MMBT3904 made byPhilips Semiconductors), a transformer T1 and a low-power low-dropoutlinear regulator U3 (TPS76050 made by Texas Instruments).

Resonant inverter 340 has a sinusoidal resonant circuit topology thatincludes four PNP transistors Q7, Q9 Q10 and Q11 (MMBT4403). In resonantinverter 340, two pairs of transistors (Q9-Q11 and Q7-Q10) are connectedso that in each pair the emitter of the first transistor drives the baseof the second transistor (i.e., a Darlington pair). These two pairs areturned ON and OFF via transformer T4 to provide an oscillating currentat a high current gain. The 16 kHz output is provided to transformer T7and to current sensor 350 and open circuit voltage sensor 360.

FIG. 17 illustrates an LED strip directly connected to an outputrectifier and filter as shown in FIG. 6. FIG. 17A illustrates a singleillumination module. Each contactless illumination module includes theelectromagnetic coupling element receiving a primary wire 210 (that is acurrent-carrying wire 210) and a secondary wire 220 inductively coupledtogether using a magnetic element 214 (preferably made of a ferritematerial). Secondary wire ends 220A and 220B are connected to an AD toDC converter providing power to LEDs, which are a DC load.Electromagnetic coupling element 232 (shown in FIG. 16) includes asecondary wire 220 wound around ferrite core 214 to form a coil, whereinsecondary wire 220 is electrically connected to provide current to theLED light sources. Ferrite core 214 is constructed and arranged toreceive current loop 210 inside the corresponding magnetic path in aremovable arrangement. Advantageously, this enables easy and convenientassembly of several illumination modules, for example inside a letterchannel. As shown in FIG. 8, several LEDs are connected together. Theabsence of a ballast resistor connected to the LEDs increases theefficiency (which may be even greater than 95%) obtained from the inputpower for the light source to produce light.

Referring to FIG. 16, electromagnetic coupling element 232 is preferablya sealed unit having the secondary wire wound around the ferrite core,with both the secondary wire and the ferrite core sealed in a waterresistant manner. Electromagnetic coupling element 232 couples theelectric power from primary wire 210 to secondary wire 220 (FIG. 16 or16A) by induction as expressed in Faraday's law. That is, the AC currentin primary wire 210 induces a voltage in coil 220 of the secondary wire,which provides electrical power delivered to the light sources. Thesecondary current is equal to the primary current divided by number ofturns. As shown in FIG. 8 or FIG. 9, primary wire 210 iselectromagnetically coupled (i.e., “proximity coupled”) to severalsecondary wires by the contactless electromagnetic coupling element, andthus primary wire 210 induces a voltage in several secondary coils woundaround the ferrite cores. The output of electromagnetic coupling element232 provides a true current source coupled to secondary wire 220. Whilecurrent loop wire 210 (i.e., the primary wire 210) is preferably locatedinside the ferromagnetic core within the magnetic flux loop, otherpositions and geometries with respect to the ferrite core may be used aslong as sufficient inductive coupling occurs.

Electromagnetic coupling element 232 (shown in detail in FIG. 17 A) alsoincludes a secondary wire wound around the ferrite core to form a coil,wherein secondary wire is connected to provide current to light sources240. Electromagnetic coupling element 232 is preferably a sealed unithaving the secondary wire wound around the ferrite core. The secondaryoutput of electromagnetic coupling element 232 provides a true currentsource.

In illumination module 202, the output from secondary wire 220 provideAC current directly to LEDs. In this AC load, one half of the LEDs ispowered on the positive cycle and the other half on the negative cycle.There is no need to use a ballast resistor coupled to the LEDs, sincethe magnetic core winding generates a true current source. The absenceof a ballast resistor connected to the LEDs increases the efficiency(which may be even greater than 95%) obtained from the input power forthe light source to produce light. The LEDs may be replaced withincandescent lamps, electroluminescent devices, or other low-voltage tomedium-voltage light sources.

Illumination module 202 includes the electromagnetic coupling elementwith a primary wire 210 and a secondary wire 220 inductively coupledtogether using a magnetic element (preferably made of a ferritematerial). Secondary wire 220 is connected to an AD to DC converter 204(FIG. 8A) providing power to LEDs; that is a DC load. Electromagneticcoupling element 232 (shown in FIG. 16) includes a secondary wire 220wound around ferrite core 214 (FIG. 16) to form a coil, whereinsecondary wire 220 is electrically connected to provide current to theLEDs. Ferrite core 214 is constructed and arranged to receive currentloop 210 inside the corresponding magnetic path in a removablearrangement. Advantageously, this enables easy and convenient assemblyof several illumination modules, for example inside a letter channel.Several LEDs are connected together. The absence of a ballast resistorconnected to the LEDs increases the efficiency (which may be evengreater than 95%) obtained from the input power for the light source toproduce light.

Referring to FIG. 16A, electromagnetic coupling element 233 includes asecondary wire 220 wound around ferrite core 215 to form a coil, whereinsecondary wire 220 is electrically connected to provide current to theLEDs. Ferrite core 215 includes a removable portion 215A formingtogether a closed magnetic path in a removable manner. The removal ofportion 215A enables accommodation of current loop 210 inside ferritecore 215 even without threading wire 210 through the opening as inferrite core 214. Advantageously, this enables easy and convenientassembly of several illumination modules.

Electromagnetic coupling element 232 (or 233) couples the electric powerfrom primary wire 210 to secondary wire 220 by induction as expressed inFaraday's law. That is, the AC current in primary wire 210 induces avoltage in coil 220 of the secondary wire, which provides electricalpower delivered to the LEDs. The secondary current is equal to theprimary current divided by number of turns.

FIG. 16A illustrates a contactless coupling element 233 having amagnetic core formed by two discrete elements 215 and 215A providing aclosed magnetic loop. Contactless coupling element 233 is suitable foruse with any one of the illumination modules shown in FIG. 8 or FIG. 9.Advantageously, current loop 210 can be placed inside ring 234 byremoving and subsequently re-attaching core element 215A with respect tocore element 215. This design allows easier and faster assembly of thesystem, where the ferrite core is arranged to receive the current loopin a removable arrangement.

FIG. 17A illustrates an illumination strip (or light module) located inletter channel 218. As described above, electromagnetic coupling element232 shown in FIG. 16, and in detail in FIG. 16A, provides contactlesscoupling (i.e., coupling without an electrical contact) to theillumination modules shown in FIG. 8 or FIG. 9.

FIG. 17B illustrates the illumination system utilizing a power supplyfor several illumination strips 230A, 230B, and 230C. Each illuminationstrips 230 can have different color light sources (for example, red,green or blue). The illumination strips may be controlled separately bycontrolling the current in the separate current loops 210A, 210B, and210C (e.g., by employing a computerized control on each loop). This way,the illumination system can generate different light effects.

FIG. 18 illustrates an illumination system 200 including severalillumination modules installed in a letter channel 218 and power supply70 (or power supply 120). The high-frequency AC voltage power supplyprovides current to an AC current loop 210, which provides power to theindividual illumination modules (shown as light strips) located inletter channel 218.

The above-described illumination systems may be used with differentillumination modules including commercially available light sources.There are several different commercially available embodiments of theLED modules. Super White STP30XC Hi-Flux StripLED® Modules may be usedalone or connected to one another, enabling configuration of channel andreverse-channel letters, signs, and displays. These modules areavailable in lengths of 6, 12, and 24 in. strips, and feature 6, 12, and24 Cool White 7,500 K Spider LEDs, respectively. Each module includes adouble-ended connector harness for daisy-chain assembly, and apre-applied strip of 3M® double-sided foam tape for peel-and-stickplacement.

Alternatively, hi-flux, interconnectable StripLED® LED modules may beused, which deliver high brightness and possess high flexibility.Specifically, LEDtronics® manufactures series STP30XC super white LEDlight strips that may be used alone or connected to one another, makingit easy to configure lighting solutions for channel and reverse-channelletters, signs, displays, under-the-counter and architecturalapplications. These light strips are available in lengths of 6-inches,12-inches and 24-inches, and they feature 6, 12 and 24 Cool White(7500K) LEDtronics SpiderLEDs, respectively. The STP306 is a 6-inch, 6LED model that uses 0.72 Watts, emits 1.2 fc and provides 29 lumens witha viewing angle of 85°. The STP324 is a 24-inch, 24 LED model that uses2.88 Watts, emits 48 fc and provides 115 lumens with a viewing angle of85°. Each module has a double-ended connector harness for easydaisy-chain assembly, and a pre-applied strip of 3M® double-sided foamtape for “peel and stick” placement. The Inter-Connector Modulefacilitates linking modules. One Inter-Connector module and one poweradapter cable are included with each light strip purchased. In additionto channel-letter applications, Strip LED may be used in buildings,amusement parks, theaters, stairways, emergency exit pathway lighting,etc. These light strips eliminate many of the shortcomings of neon orfluorescent lamps such as heat, broken tubes and ballast failures.

FIGS. 19 and 19A illustrate a coupling box 400 for use with theillumination systems shown in FIG. 8, 9 or 11. Coupling box 400 two boxparts 402 and 404 coupled with a hinge 406. Box part 402 includes amagnetic core 410 with an opening 408 for receiving current loop 210.Box part 404 includes a magnetic core 412. The two box parts 402 and 404are cooperatively designed to provide a closed magnetic loop by placingmagnetic core 412 in contact with magnetic core 410, when the box parts402 and 404. This design enable quick and easy placement of current loop210 inside the magnetic core for proper electromagnetic coupling. Areturn current loop 210 is located outside of the magnetic core.Coupling box 400 includes a transformer and a rectifier and a capacitor.Wires 220A and 220B are connected to an LED strip.

FIGS. 19B and 19C illustrate schematically a magnetic core and locationsof secondary wires inside the coupling box shown in FIGS. 19 and 19A.The magnetic core includes split core elements 410 and 412. As shown inFIG. 19B, split core element 410 is designed to receive a bobbin 415 forthe secondary wires. As shown in FIG. 19C, split core element 410 isdesigned to receive a PCB board 419 for the secondary wires split coreelement 410 is designed to receive a PCB board 419 with a copper traces419 fabricated on PCB 417 to provide the secondary wires.

FIGS. 20, 20A, 20B and 20C illustrate different embodiments of thecoupling boxes designed for the illumination system shown in FIG. 8, 9or 11, and used for the landscaping. In this design, rod 428 is coupledvia connector 425 to box 420 receiving the electric wires. Coupling ring430 is connected to the illumination fixture 432 for purposes ofillumination using LEDs. FIG. 12C illustrates a dual clip design for ahigher output such as driving three LED groups.

Although this system gains some complexity compared to thesingle-channel structure, several technical challenges are easilyresolved. There are several possible problems such as:

(1) The series-resonant stage uses the combined leakage inductance ofthe transformers as a resonant element. This saves one component.

(2) The transformers can be built very easily in a way that reducesinterwinding capacitance and increases the needed leakage inductance,while ensuring full safety isolation.

(3) Resonant topology allows for extremely efficient conversion withreduced EMI emissions.

(4) The resonant topology here functions at fixed frequency; thus,magnetic components can be optimized. Operation is in open loop; thus noadded control loops are needed.

(5) Short circuit conditions are not a problem since the input of theresonant converter is a flyback output stage with reduced capacitance,acting as a limited current source.

(6) Dimming, using the bypass method described earlier can still beapplied. It can also be applied to any number of channels independentlyof the others.

(7) The flyback stage is no longer safety-isolated. Thus, theconstruction can be simplified significantly, while decreasing leakageinductance to further reduce losses.

(8) Capacitor C_(DC) is not strictly necessary, but can be easily addedin order to clamp residual leakage energy from the flyback circuit.

Importantly, the proposed circuits eliminate the need for electrolyticcapacitors in low-cost LED string drivers. This is done by drivingconcurrently a boost cell and a flyback cell, while utilizing a singlecontrol loop and a single main switching element. An important addedfeature of this topology is the improved dynamic behavior, which enablesa simple and effective dimming technique.

For larger systems, the integration with a series-resonant circuitallows a seamless expansion to multi-channel operation is order to meetregulatory safety requirements.

While the present invention has been described with reference to theabove embodiments and the enclosed drawings, the invention is by nomeans limited to these embodiments. The present invention also includesany modifications or equivalents within the scope of the followingclaims.

What is claimed is:
 1. An illumination system, comprising: a powersupply including a boost converter operating in the discontinuousconduction mode, a flyback converter operating in the criticalconduction mode, and a switch coupled to said flyback converter; andseveral light emitting diodes receiving power from said power supply. 2.The illumination system of claim 1 wherein said flyback converterincludes a flyback inductor, a second switch, and a flyback diodeproviding flyback-based output regulation and isolation; and whereinsaid first-mentioned switch and said second switch are connected to turnon at complete discharge of said flyback inductor.
 3. The illuminationsystem of claim 2 wherein said flyback converter includes a flybackinductor, a second switch, and a flyback diode providing flyback-basedoutput regulation and isolation; and wherein an output from said flybackconverter is coupled to an output rectifier and a filter providing anLED current to said several light emitting diodes.
 4. The illuminationsystem of claim 1 wherein all capacitors are non-electrolyticcapacitors.
 5. The illumination system of claim 1 wherein said flybackconverter includes a capacitor operating in open loop and thus saidpower supply is controlled without receiving a feedback from saidcapacitor of said flyback converter.
 6. The illumination system of claim1 wherein said flyback converter provides an output being regulated by afeedback loop.
 7. The illumination system of claim 6 wherein saidflyback converter is regulated by said feedback loop being a voltagefeedback.
 8. The illumination system of claim 6 wherein said flybackconverter is regulated by said feedback loop being a current feedback.9. The illumination system of claim 6 wherein said boost converterincludes a boost inductor and a boost diode, and said flyback converterincludes a flyback inductor and a flyback diode, and wherein saidflyback converter is regulated by said feedback loop and an error signalsets a peak current of said flyback inductor that automatically alsodetermines a current flowing in said boost inductor.
 10. An illuminationsystem, comprising: a power supply including a boost converter operatingin a discontinuous conduction mode, a flyback converter operating in acritical conduction mode, and a switch coupled to said flybackconverter, wherein said boost converter includes a boost inductor and aboost diode, and said flyback converter includes a flyback inductor anda flyback diode and said power supply is constructed to turn on saidswitch as the current flowing in said flyback inductor reaches zerovalue; and several light emitting diodes receiving power from said powersupply.
 11. The illumination system of claim 10 wherein all capacitorsare non-electrolytic capacitors.
 12. The illumination system of claim 10wherein an output of said flyback converter is used for regulating saidpower supply.
 13. The illumination system of claim 10 wherein saidflyback converter includes a capacitor operating in open loop and thussaid power supply is controlled without receiving a feedback from saidcapacitor of said flyback converter.
 14. The illumination system ofclaim 10 wherein said flyback converter provides an output beingregulated by a feedback loop.
 15. The illumination system of claim 14wherein said flyback converter is regulated by said feedback loop beinga voltage feedback.
 16. The illumination system of claim 14 wherein saidflyback converter is regulated by said feedback loop being a currentfeedback.
 17. The illumination system of claim 14 wherein said flybackconverter is regulated by said feedback loop and an error signal sets apeak current of said flyback inductor that automatically also determinesa current flowing in said boost inductor.
 18. An illumination method,comprising the steps of: providing a power supply including a boostconverter, a flyback converter, and a switch coupled to said flybackconverter; operating said boost converter in the discontinuousconduction mode, and operating said flyback converter in the criticalconduction mode; and delivering current to several light emittingdiodes.
 19. The illumination method of claim 18 including turning onsaid switch as a current flowing in a flyback inductor of said flybackconverter reaches zero value.
 20. The illumination method of claim 18including regulating said power supply by an output of said flybackconverter.
 21. The illumination method of claim 18, wherein said flybackconverter includes a capacitor operating in open loop and thuscontrolling said power supply without receiving a feedback from saidcapacitor of said flyback converter.
 22. The illumination method ofclaim 21 including regulating the output from said flyback converter byutilizing a feedback loop.
 23. The illumination method of claim 22including setting a peak current of said flyback inductor by an errorsignal sets that automatically also determines a current flowing in aboost inductor of said boost converter.
 24. A power supply comprising: aboost converter including a boost inductor and a boost diode andoperating in the discontinuous conduction mode; a flyback converterincluding a flyback inductor and a flyback diode and operating in thecritical conduction mode; and a switch coupled to said flyback converterand being connected to turn on at complete discharge of said flybackinductor for said operation in the critical conduction mode.
 25. Thepower supply of claim 24 including a second switch, and wherein saidfirst-mentioned switch and said second switch are connected to turn onas the current flowing in said flyback inductor reaches zero value. 26.The power supply of claim 25 wherein all capacitors are non-electrolyticcapacitors.
 27. The power supply of claim 25 wherein said flybackconverter includes a capacitor operating in open loop and thus saidpower supply is controlled without receiving a feedback from saidcapacitor of said flyback converter.
 28. The power supply of claim 25wherein said flyback converter provides an output being regulated by afeedback loop.
 29. The power supply of claim 28 wherein said flybackconverter is regulated by said feedback loop being a voltage feedback.30. The power supply of claim 28 wherein said flyback converter isregulated by said feedback loop being a current feedback.